1. Field of the Invention
The present invention relates to a protein which binds to a stress responsive element and regulates the transcription of genes located downstream of the element; a gene coding for the above protein; a recombinant vector comprising the gene; a transformant comprising the recombinant vector; a transgenic plant comprising the gene; a method for producing the above protein using the transformant; and a method for determining a stress level in a plant.
2. Prior Art
Transcription of genes is performed by RNA polymerase. RNA polymerase synthesizes ribonucleoside phosphates in the 5′ to 3′ direction using double-stranded DNA as a template in a primer independent manner. In the case of Escherichia coli, for example, its RNA polymerase takes the form of a holoenzyme in which ρ factor having promoter recognition ability is bound to the core enzyme β′βα2. This RNA polymerase initiates transcription and elongates RNA chain; the transcription is terminated by the binding of ρ factor. On the other hand, in the case of eucaryotes, RNA polymerase is classified into RNA polymerases I, II and III, any of which has a complicated structure composed of more than 10 subunits. RNA polymerase I selectively transcribes rRNA; RNA polymerase II selectively transcribes mRNA precursor; and RNA polymerase III selectively transcribes tRNA and 5SrRNA. The amount of RNA synthesized by such RNA polymerase varies widely depending on the growth stage of the relevant cells and environmental changes around them. A transcription factor which positively or negatively regulates the transcription initiation of RNA polymerase is deeply involved in the variation in the amount of RNA synthesis.
Generally, living cells are exposed to an external environment composed of a number of factors including temperature, pressure, oxygen, light, radioactive rays, metal ions, organic compounds, etc. When these factors vary, cells perceive such changes as stress and make characteristic responses to them. For example, cells exhibit a response called “heat shock response” to high temperatures. From this response, the expression of a group of heat shock proteins (HSPs) is induced. HSPs prevent the irreversible precipitation of heat-denatured proteins and have the function of molecular chaperone that facilitates the refolding of such proteins, thereby protecting cells from heat stress. It is known that a transcription factor called “heat shock factor (HSF)” plays an important role in the manifestation of the above-described heat shock response in human, Xenopus, Drosophila, etc. [Kazuhiro Nagata, Cell Technology, 10:348–356 (1991)]. When activated by heat shock, HSF binds to heat shock element (HSE) located upstream of a gene coding for HSP (also known as heat shock gene) to thereby promote the transcription of the heat shock gene.
On the other hand, it is also reported that plants induce stress proteins such as LEA proteins, water channel proteins or synthetases for compatible solutes in their cells when they are exposed to stress such as dehydration, low temperature, freezing or salt, thereby protecting their cells from such stress. However, much more research is required to elucidate transcription factors which regulate the transcription of genes encoding those stress proteins.